1. Field of the Invention
The invention generally relates to a digital video channel broadcasting system comprising a transmitter and a multiplicity of receivers and, more particularly, to a method and subsystem for use in such a system for effectively transmitting and receiving program information while reducing the electric power consumed for program information reception in each receiver.
2. Description of the Prior Art
In a digital television broadcasting system such as a satellite broadcasting, a CATV (cable television) system, etc., a broadcasting station or transmitter periodically transmits program information by including the program information in a transport stream, which comprises time-division multiplexed program data for a plurality of channels. The program information is received and stored by television receivers for displaying a program guide in response to a user's request. However, a program may be changed and a special or emergency broadcast may be delivered at any time. For this reason, in order to cope with the changes in program and special or emergency broadcasts, television (TV) receivers have to keep on receiving the program information even when no channel is viewed, causing the electric power consumption of each TV receiver to be increased.
Japanese unexamined patent publication Hei.9-275,530 discloses "TELEVISION RECEIVER" as a solution to this problem. In the TV receiver, a controller is always supplied with electric power. A first power supply to a tuner and a signal processing circuit and a second power supply to an audio circuit, a driver circuit, a display device and a loudspeaker are controlled by the controller. The electronic program guide (EPG) is received only at times preset by the user, in which only the first power supply is effected. Both the first and second power supplies are effected during the user viewing a program, and none of them is effected otherwise.
However, if any change in the EPG has been made after the last time of EPG reception, the change will not be reflected in a TV program schedule displayed by a command from the user. Further, any special or emergency broadcast which is not included in the last EPG data is missed in the above-cited prior art.
It is an object of the invention to provide a digital TV transmitter and a receiver that ensures the reception of program information and any irregular program while saving the power consumption in the receiver.
Generally speaking, only a part of EPG data has been changed even in EPG data received at a relatively long interval such as several hours. Therefore, it is not efficient to update all of the stored program information each time of EPG data reception.
It is another object of the invention to provide a digital TV transmitter and a receiver that saves the power consumption in the receiver by updating only data portions of the stored program information which include changed EPG data.
If a receiver has a memory with a capacity insufficient to store all of the received EPG data, it will take some time to collect EPG data which has not stored in the memory and to display program information in response to a program schedule display command from the user.
It is still another object of the invention to provide a digital TV transmitter and a receiver that first displays programs of higher priorities which have been stored in nonvolatile memory and then displays programs of lower priorities which have been received after the detection of a program information display command for providing a quick response.